A number of processes are known which take place under conditions of reduced pressure. Examples include plasma cleaning, sputtering and vaporising. The material to be treated is often in the form of a sheet.
In International patent specification WO 91/17561 (Eastman Kodak) an apparatus for the plasma treatment of material in continuous form under vacuum is described. The apparatus comprises a housing defining a treatment cell having a sheet material path extending therethrough from an entrance to an exit, the entrance and exit each being closed by a roller pair. A vacuum is applied to the treatment cell.
The sealing of the rollers to the housing is an important feature if desirable consistent conditions of reduced pressure in the treatment cell are to be achieved. In the apparatus described in W091/17561, the rollers are sealed to the housing by the use of fixed sealing members. We have found that the use of fixed sealing members is often unsatisfactory, leading to undesirable leakages.
In European patent specification EP 0 384 041-A, (Agfa-Gevaert NV), a process is described for the coating of a web support under vacuum conditions with a layer of vapour depositable material followed by the lamination of the coated material with a protective organic resin layer.
Although the process described operates satisfactorily, the apparatus used requires both the vapour deposition and the lamination to take place in the same vacuum chamber. This chamber is therefore of a considerable volume, requiring the consumption of significant energy and time during start-up. Furthermore, once a batch of web support has been so coated and laminated, it can only be removed by releasing the vacuum to enable the chamber to be opened. Time and energy is therefore repeatedly wasted in shut-down and start-up of the apparatus.